The invention pertains to means for determining the water content of bulk materials and more particularly the use of a neutron source increasing the sensitivity of a nuclear gage in the measurement of water content of bulk material such as for example the water content of plastic concrete.
Methods are needed for measuring the amount of constituent materials, such as cement and water, in freshly mixed concrete in order to predict the final quality of the hardened concrete. At the present time, the quality control of concrete ordinarily is exercised prior to placement by inspectors who oversee the weighing-in and mixing of the cement, aggregates, admixtures, and water at batching sites. In addition, the quality of the end-product concrete is established by tests on cured specimens such as strength cylinders days and weeks after placement. Post-placement tests on cylinders which indicate strengths below specification minimums have the disadvantage that removing the hardened substandard concrete on the job site is difficult and uneconomical.
Fast neutron scattering techniques have been used for determining the water or organic content of bulk materials and especially for determining the water content in soils. The phenomenon upon which these gages are based is that high energy or fast neutrons lose a much greater fraction of their initial energy when scattered by hydrogen atoms than by atoms of any other element. The resulting low energy or thermal neutrons can then be counted by a detector which is primarily sensitive to them. This principle has been used, for example, in determining the water content of soils and in the present invention is applied to the measurement of the water content in plastic concrete.